1. Field of the Invention
The present invention relates to techniques for enabling high-resolution multi-touch sensing based on frustrated total internal reflection.
2. Description of the Related Art
Touch sensing is commonplace for single points of contact. One group of touch sensing techniques is to employ frustrated total internal reflection (FTIR). When light encounters an interface to a medium with a lower index of refraction (e.g. glass to air), the light becomes refracted to an extent that depends on its angle of incidence, and beyond a certain critical angle, it undergoes total internal reflection (TIR). Fiber optics, light pipes, and other optical waveguides rely on this phenomenon to transport light efficiently with very little loss. However, another material at the interface can frustrate this total internal reflection, causing light to escape the waveguide there instead.
Frustrated total internal reflection is well known and has been used in the biometrics community to image fingerprint ridges since at least the 1960s. U.S. Pat. No. 3,200,701 to White, incorporated herein by reference, issued in 1965 and describes using FTIR to optically detect the ridge pattern of a skin surface.
U.S. Pat. No. 3,673,327 to Johnson et al., incorporated herein by reference, issued in 1972 and discloses an early version of a touch actuable device in which a binary device detects the attenuation of light through a platen waveguide caused by a finger in contact.
U.S. Pat. No. 3,846,826 to Mueller, incorporated herein by reference, issued in 1974 and describes an imaging touch sensor that allows a user to “paint” onto a separate display using free-form objects, such as brushes, styli and fingers. In that device, light from the flying spot of a CRT is totally internally reflected off the face of a large prism and focused onto a single photo detector, thereby generating an updating bitmap of areas that are being contacted. In 1985, this method was updated in an optically inverted configuration, with a video camera and a broad light source replacing the CRT and photodetector, as disclosed in Greene, R., “The Drawing Prism: A Versatile Graphic Input Device,” Proceedings of the 12th Annual Conference on Computer Graphics and Interactive Techniques SIGGRAPH '85, ACM Press, New York, N.Y., 103-110 (1985), incorporated herein by reference.
U.S. Pat. No. 4,346,376 to Mallos, incorporated herein by reference, discloses a CRT-based touch sensor, which replaced the bulky prism with a thin platen waveguide and operates by detecting the light scattered away by an object in optical contact. More recent fingerprint sensors use this approach, as disclosed in Fujieda, I., Haga, H., “Fingerprint Input based on Scattered-Light Detection,” Applied Optics-IP, 36, 35, 9152-9156 (1997), incorporated herein by reference.
The robotics community also has used this approach since 1984 in the construction of tactile sensors for robot grippers, but with a compliant surface overlay. Various publications include: Mott, D. H., Lee, M. H., and Nicholls, H., “An Experimental Very High Resolution Tactile Sensor Array,” Robot Sensors Vol. 2: Tactile and Non-Vision, Pugh, A., Ed. Springer-Verlag, Berlin, 179-188 (1986); Tanie, K., Komoriya, K., Kaneko, M., Tachis, S., and Fujikava, A., “A High Resolution Tactile Sensor,” Robot Sensors Vol. 2: Tactile and Non-Vision, Pugh, A., Ed. Springer-Verlag, Berlin, 189-198 (1986); and U.S. Pat. No. 4,668,861 to White, each of which is incorporated herein by reference.
With the use of a compliant surface overlay, a structured flexible membrane, normally kept apart from the waveguide by an air-gap, makes optical contact with the waveguide when depressed. U.S. Pat. No. 4,484,179 to Kasday, incorporated herein by reference, discloses this approach in the context of a touch sensitive display.
One fairly straightforward approach for sensing multiple points of contact simultaneously or “multi-touch sensing” employing non-FTIR based methods is to utilize multiple sensors, with each sensor sensing a respective point of contact. For example, Tactex Control Inc. has a line of array sensors for use as floor sensors, security devices and other applications. As another example, the publication Lee, S., Buxton, W., and Smith, K. C., “A Multi-Touch Three Dimensional Touch-Sensitive Tablet,” Proceedings of the SIGCHI Conference on Human Factors in Computing Systems (San Francisco, Calif., United States), CHI '85. ACM Press, New York, N.Y., 21-25 (1985), incorporated herein by reference, describes the use of sensors arranged in a matrix configuration with an active element (e.g. diode, transistor) disposed at each node.
Multi-touch sensing may be achieved by employing a passive matrix of sensing elements, such as force-sensitive-resistors (FSRs), as discussed in Hillis, W. D., “A High Resolution Imaging Touch Sensor,” International Journal of Robotics Research, pages 1, 2, 33-44 (1982), incorporated herein by reference. U.S. Pat. No. 4,134,063 to Nicol et al., incorporated herein by reference, discloses the use of capacitive electrodes for this purpose. And more recently discussed in Rekimoto, J., “SmartSkin: An Infrastructure for Freehand Manipulation on Interactive Surfaces,” Proceedings of the SIGCHI Conference on Human Factors in Computing Systems, CHI '02, ACM Press, New York, N.Y., 113-120 (2002), incorporated herein by reference. The Fingerworks iGesturePad is another example of a device that employs a passive matrix of capacitance sensors. U.S. Pat. No. 6,323,846 to Westerman et al., incorporated herein by reference, discloses additional examples of using such an array in a multi-touch surface system. Such systems, while less complex than systems that employ multiple active sensors, still entail numerous electrical connections and thus disadvantageously limit their application to uses that require relatively low resolution (e.g., under 100×100). Furthermore, such systems are visually opaque and thus require the use of top-projection if to be integrated with a graphic display.
The use of video cameras has been proposed to acquire high-resolution datasets at rapid rates. However, these machine vision based techniques are quite imprecise and are not able to determine if true touch contact has been made, a disparity that can be quite disturbing to the user. Recent approaches include estimating depth from intensity as discussed in Matsushita, N. and Rekimoto, J., “HoloWall: Designing a Finger, Hand, Body, and Object Sensitive Wall,” Proceedings of the 10th Annual ACM Symposium on User Interface Software and Technology (Banff, Alberta, Canada, Oct. 14-17, 1997), UIST '97, ACM Press, New York, N.Y., 209-210 (1997); estimating depth from stereo as disclosed in Wilson, A. D., “TouchLight: An Imaging Touch Screen and Display for Gesture-Based Interaction,” Proceedings of the 6th International Conference on Multimodal Interfaces (State College, Pa., USA, Oct. 13-15, 2004), ICMI '04, ACM Press, New York, N.Y., 69-76 (2004); Malik, S. and Laszlo, J., “Visual Touchpad: A Two-Handed Gestural Input Device,” Proceedings of the 6th International Conference on Multimodal Interfaces (State College, Pa., USA, Oct. 13-15, 2004), ICMI '04, ACM Press, New York, N.Y., 289-296 (2004); and tracking markers embedded within a deformable substrate as disclosed in Kamiyama, K., Vlack, K., Mizota, T., Kajimoto, H., Kawakami, N., and Tachi, S., “Vision-Based Sensor for Real-Time Measuring of Surface Traction Fields,” IEEE Comput. Graph. Appl. 25, 1 (January 2005), 68-75. Each of these references is incorporated herein by reference.
Additional publications that set forth various interaction techniques include: Buxton, W., Hill, R., and Rowley, P., “Issues and Techniques in Touch-Sensitive Tablet Input,” Proceedings of the 12th Annual Conference on Computer Graphics and Interactive Techniques SIGGRAPH '85, ACM Press, New York, N.Y., 215-224 (1985); Dietz, P. and Leigh, D., “DiamondTouch: A Multi-User Touch Technology,” Proceedings of the 14th Annual ACM Symposium on User Interface Software and Technology (Orlando, Fla., Nov. 11-14, 2001), UIST '01. ACM Press, New York, N.Y., 219-226 (2001); Westerman, W., Elias, J. G., and Hedge, A., “Multi-Touch: A New Tactile 2-D Gesture Interface for Human-Computer Interaction,” Proceedings of the Human Factors and Ergonomics Society 45th Annual Meeting (Minneapolis/St. Paul, Minn., October 2001), 632-636 (2001); and Wu, M. and Balakrishnan, R., “Multi-Finger and Whole Hand Gestural Interaction Techniques for Multi-User Tabletop Displays,” Proceedings of the 16th Annual ACM Symposium on User Interface Software and Technology (Vancouver, Canada, Nov. 2-05, 2003), UIST '03, ACM Press, New York, N.Y., 193-202 (2003), each of which is incorporated herein by reference.